When tunneling magnetoresistive sensors are manufactured, a free layer and a barrier layer are adjacent a ferromagnetic layer. In known tunneling magnetoresistive sensors, the ferromagnetic layer has a surface roughness that is undesirably high for optimum performance of subsequently applied layers.
When the barrier layer is applied over this rough surface on the ferromagnetic layer, it is necessary to increase the thickness of the barrier layer to an undesirably high thickness to ensure that the barrier layer will be free of holes or other defects that could otherwise result in an electrical breakdown between the ferromagnetic layer (which is typically at a reference potential) and the free layer (which is typically at voltages other than the reference potential). Even with this increased thickness, the high roughness of the ferromagnetic layer is replicated, at least in part, in increased roughness of the top surface of the barrier layer. When the free layer is applied adjacent the barrier layer, the free layer also has increased roughness, resulting in undesired unit-to-unit variation of tunneling resistance of the barrier layer, and general decreased performance characteristics of the tunneling magnetoresistive sensor.
There is thus a problem with finding a material composition for a magnetic layer that provides desired magnetic properties, while at the same time providing a reduced surface roughness for the magnetic layer. A process and a magnetic material composition are needed which avoid undesired high surface roughnesses in various layers of the stack.
Embodiments of the present invention provide solutions to these and other problems, and offer other advantages over the prior art.